After Friday morning's Apple press conference about the iPhone 4 and its antenna issues, Apple executives took a small group of journalists (11 all told, including myself) on a tour of the company's wireless-testing facilities.

We were, the executives said, the first outsiders allowed into the area, a spot off-limits to most Apple employees. Even our escorts from Apple's PR department said they hadn't been in there before.

On a sunny and hot day in Silicon Valley, we were led through the centre of Apple's campus and then across the street to the building housing the testing area. Behind a series of heavy security doors, we met Ruben Caballero, a senior Apple engineer and wireless expert. (Caballero, you might remember, was the subject of a Bloomberg report on Thursday suggesting that he had warned Steve Jobs about antenna problems in advance of the iPhone 4's release - a report referred to by Steve Jobs on Friday as "total bullshit.")

Apple's secret product labs

The point of the tour was clear: to show that Apple takes the testing of wireless issues very seriously, and that suggestions that the company was simply sleeping on the job when it came time to test the iPhone 4 are misguided.

Despite being a guy who obviously spends most of his time behind closed doors working on fiendishly complex radio engineering problems, Caballero proved to be an excellent tour guide, answering reporters' questions with enthusiasm.

As he welcomed us into his lair, Caballero pointed out that many of the workbenches around us were draped with black fabric. "This is what we call a black lab," he said, meaning that they're testing secret stuff.

"We have to cover all the benches when anyone comes in, even people from within Apple."

"The existence of this lab used to be secret," an Apple PR representative pointed out.

"Now it's not."

Apple Wireless Test Chamber

Not since Steve Jobs showed detailed pictures of it to members of the press a few hours earlier, anyway. Apple has since also posted a page about its test methods, including a video overview.

Apple's wireless lab has 16 different anechoic chambers - think of them as bank vaults, padded with foam shaped into pointy cones to stop all reflections, designed to create completely radio-neutral environments - at a cost Caballero estimated at $1.2 million per chamber.

"It was very simple in the old days," Caballero said, "when you had one antenna and one frequency."

He pointed out that his first radio project involved a bunch of antennae on a football field. But these days, he pointed out, phones have in-built antennae, four GSM frequency bands, four UMTS frequency bands, they're sending and receiving massive amounts of data, there's Wi-Fi and Bluetooth and GPS as well - it's complicated.